Skip to main content

Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

See other formats

GALIANO AND BLACK GLACIERS                              81
in 1909. Well within the mountain valley the marginal valley disappears, the glacier merging into talus from the mountain, and still higher into snow fans where snow has &valanched down the mountain sides in such masses that summer melting at that elevation is incapable of removing it. The marginal valleys and the marginal streams present some interesting features which are described in later pages.
Beyond the mountains the Galiano Glacier expands into a piedmont bulb more than double the width of the valley glacier. It does not expand westward to a great extent, 'Chiefly because the mountain wall extends farther out in that direction, but partly because it is trimmed on that side by the large glacial stream that flows down the western marginal valley and then turns eastward to enter Yakutat Bay. This expanded bulb is completely covered with ablation moraine, and in the outer portion ice can be seen in only a few small patches; in fact in the extreme eastern part we were unable to find any ice, though its presence was confidently inferred from the height of the moraine, its irregular surface, and the great amount of cold water that emerges from it. The margin of the ice bulb is an irregular, hummocky embankment whose base is essentially at sea level, and whose eastern end lies just back of the beach. The surface of the ice bulb is a maze of hummocks and depressions with the roughly crescentic arrangement so typical of ablation moraines on expanded piedmont bulbs. That this glacier had the same general condition in 1890 as in 1909 is proved both by Russell's photographs and by his description. He says "Debris-covered ice streams, too small to reach the water, are typical of a large class of glaciers in southern Alaska, which are slowly wasting away and have become buried beneath de"bris concentrated at the surface by reason of their own melting. The Galiano Glacier is a good example of this class." l
Along the southern base of the glacier bulb an alluvial fan is being built up by the stream from the western margin of the Galiano and to a lesser degree by small streams that issue from the glacier front. Beyond this, during the period of our observation, was a series of low morainic hummocks between which flow the distributaries of Esker Stream from the Atrevida Glacier. There is good reason for believing that ice still exists beneath this entire area and that, in reality, what seems to be the terminus of the Galiano Glacier bulb, as described above, is only the margin of a part of the glacier which remains higher than the rest because of a more recent supply of ice and of its protection from ablation by the morainic cover. The depressed area of the piedmont bulb beyond the apparent front of the glacier is interpreted, in part at least, as an interior flat, lowered by melting until it became the seat of alluvial fan deposit; but the area beyond this portion, which consists of morainic hummocks, probably represents the moraine-covered outermost portion of the piedmont bulb. The Galiano Glacier is believed to expand beyond the mountain front into a bulb with many tunes the area of that which is now visible, and to reach five miles or more from the mountain base, attaining a width of two or three miles in its broadest portion. That the bulb is not wider is due to the fact that it forms the shore of this part of Yakutat Bay, and has, therefore, been cut off on the eastern side.
This interpretation of conditions in front of the visible piedmont bulb of the Galiano Glacier is based upon a number of facts, the most significant of which are a series of notable changes in condition between 1890 and 1905, and between 1905 and 1909. These changes affected both the visible piedmont area and the region to the south of it. Their
i Russell I. C., An Expedition to Mount St. Elias, Alaska, Nat. Geog. Mag., Vol. IE, 1891, p. 101. a